More than 60,000 people – civilians, Syrian troops and rebels – have been
killed in the country's bitter civil war the United Nations announced, a
toll it described as "truly shocking".

The new calculation, the result of a five-month UN project to cross-reference names of the dead, suggests that previous analysis of the carnage caused by almost two years of protests, repression, and fighting issued by opposition groups were too conservative.

Even the new figure is likely to be an underestimate, the United Nations High Commissioner for Human Rights suggested, as it ignores incidents with incomplete accounts of victims and cannot include those who have been "disposed of" secretly, without their families being informed.

It means the Syrianwar is now twice as bloody as that which put an end to the regime of Col Muammar Gaddafi in Libya last year, despite – or as many critics will now start to say because of – the latter's involvement of concentrated Nato air power.

John McCain, the former United States presidential candidate who has urged President Barack Obama to intervene in the conflict, referred to the figures on his Twitter account yesterday and said the president's policy was no longer "leading from behind" but "waiting from behind".

The UN high commissioner, Navi Pillay, said: "The failure of the international community, in particular the Security Council, to take concrete actions to stop the bloodletting shames us all. Collectively, we have fiddled at the edges while Syria burns."

The bald figures of the death totals, initially put out by overseas-based activist groups like the Syrian Organisation for Human Rights and the Syrian Network for Human Rights, show the speed with which the uprising escalated into all-out war in 2012.

From the beginning of the uprising – usually dated to the first repression of protests in the southern city of Deraa on March 15, 2011 – it took nine months, until December of that year, for the number of dead to reach 5,000.

The next 5,000 were killed in the subsequent five months, including hundreds in February in the shelling of rebel districts of Homs, the first major siege. From then on, roughly 5,000 people have died every month.

Ms Pillay said the new study had cross-referenced names put out by seven sources, including the Syrian government and activist groups, and eliminated overlaps to come up with a list of 59,648 dead by November 30.

"Given there has been no let-up in the conflict since the end of November, we can assume that more than 60,000 people have been killed by the beginning of 2013," she said. "The number of casualties is much higher than we expected, and is truly shocking."

Libyan government estimates reckon that around 30,000 people, including Gaddafi regime troops, rebels and civilians, died in the 2011 war there.

With forces loyal to President Bashar al-Assad, who is always said to have had one of the best-equipped armies in the Arab world, continuing to use all their firepower against a slowly advancing opposition, there is little sign that the death toll will tail off significantly in the coming months.

The fear is that even if President Assad steps down, Syria could descend into the sort of sectarian war that disfigured Lebanon in the 1970s and 80s, which led to an estimated 150,000 deaths. By comparison, the Iraq Body Count, a group that lists victims of conflict since the coalition invasion to topple Saddam Hussein in 2003, on Tuesday said it had recorded between 110,937 and 121,227 civilian deaths in almost ten years up to the end of 2012, to which can be added an estimated 45-50,000 combatant deaths.

The bloodshed in Syria continued yesterday, most notably when a government air strike on rebels in the eastern Ghouta district of Damascus province hit a petrol station, killing at least 12 people including opposition fighters and possibly up to 50, according to a number of activist groups.

Fighting also continued around Aleppo airport, while rebels launched a third major attack on the key regime airbase at Taftanaz, between Aleppo and Idlib, which is all but surrounded and yet has fought off a number of such assaults in recent months.